package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> query = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<E>) query;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if(objects.size()==1){
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(),
                new Class[]{mapperClass}, new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        // 在invoke方法中借助method对象来获取到当前执行的方法名以及当前方法所在类的全限定类名
                        String methodName = method.getName();
                        String className = method.getDeclaringClass().getName();
                        String statementId = className + "." + methodName;

                        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                        String sqlType = mappedStatement.getSqlType().toUpperCase();
                        if ("INSERT".equals(sqlType) || "DELETE".equals(sqlType) || "UPDATE".equals(sqlType)) {
                            return executeUpdate(statementId, args);
                        }

                        // 获取被调用方法的返回值类型
                        Type genericReturnType = method.getGenericReturnType();
                        // 判断是否进行了 泛型类型参数化
                        if (genericReturnType instanceof ParameterizedType) {
                            List<Object> objects = selectList(statementId, args);
                            return objects;
                        }

                        return selectOne(statementId, args);
                    }
                });

        return (T) proxyInstance;
    }

    @Override
    public Boolean executeUpdate(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        Boolean flag = simpleExecutor.executeUpdate(configuration, mappedStatement, params);
        return flag;
    }
}
